Many types of machines such as construction equipment and watercraft have mechanisms, the positions of which need to be changed from time to time as the machine is operated. For example, construction "dozers" and agricultural tractors usually employ hydraulic valves, the mounted location of which is well removed from the location of the machine operator. However, the operator needs to change the valve position from time to time to, e.g., raise a dozer blade, lower a plow or the like.
Many types of watercraft, e.g., pleasure and commercial vessels, present a similar requirement. The helmsperson is required to manipulate steering linkages, engine throttles and the like from the remotely-located vessel helm. Commercial buses have similar requirements in that the driver must control the throttle of the engine (which may be at the rear of the bus) or control the transmission using a nearby foot treadle or control handle, respectively.
Remote control cables (and seals used therewith) have been used for decades for such purposes. A common type of control cable has an outer "conduit" which is held stationary by anchoring it with a clamp or to a bulkhead or the like. An inner "core" is spaced from and movable with respect to the conduit. Often, lubricant is applied between the conduit and the core to reduce friction. A "dynamic seal," i.e., one sealing between the stationary cable sleeve and the moving, rigid rod portion of the core, is used to confine the lubricant in the cable and exclude airborne dirt particles.
In a typical application, the rigid rod at one end of such core is coupled to a control handle or steering mechanism manipulated by the machine operator. The other end of the core is coupled (also by using a rod or the like) to that which is being remotely controlled, e.g., a hydraulic valve, engine throttle or outboard motor steering linkage. When the control handle is manipulated, the core is "pushed" or "pulled." That is, the core is placed in compression or tension, respectively.
Such remote control cables are ideal in many applications since they are generally straightforward in application (as compared to electronic controls, for example) and relatively easy to maintain. A leading manufacturer of such remote control cables is Morse Controls Division of IMO Industries, Inc., Hudson, Ohio.
Notwithstanding the enormous acceptance of such remote control cables, they are not without problems. One relates to a physical characteristic known as "column strength" which is a factor limiting the compressive force which can (or at least should) be applied to the core when the core is pushed. Column strength is a limitation since if too much compressive force is applied, the core tends to deform by "kinking" or buckling and/or to be urged to "sliding-friction-contact" with the inner surface of the conduit. As a result, the remote control arrangement may operate only by applying excessive force to the control handle.
Another disadvantage involves the core-conduit lubricant. Lubricants prior used in such applications tend to create more "drag" than is desired. And the configuration of the dynamic seal is such that the lubricant leaks past the seal to the exterior of the rod. Such leaked lubricant attracts airborne dirt particles which, in turn, can migrate into the cable and shorten its life, sometimes materially. Or the dynamic seal is inadequate to satisfactorily exclude such dirt, even if no leaking lubricant is present.
Earlier efforts to resolve the leakage and dirt migration problems have involved seals which "squeeze" against the moving rod very tightly and/or have a large surface area contacting such rod. Seals of the former type tend to wear quickly and either approach increases the effort required to manipulate the control handle and diminishes the positioning accuracy with which such manipulation is performed. And if the seal is sufficiently "loose" against the rod to reduce operating effort to an acceptable level, such seal does a less-than-exemplary job of sealing lubricant inside the cable while excluding dirt.
Yet another disadvantage of known control cables involves the conduit, the core and a physical phenomenon known as the "coefficient of friction" between such conduit and core. Generally speaking, the effort required to manipulate a control handle is proportional to the coefficient of friction with higher coefficients resulting in greater effort.
Coefficients of friction are of two types. One is the "static" coefficient of friction, i.e., that between the core and conduit when the core is stationary but being urged to move. The "dynamic" coefficient of friction (or sliding coefficient of friction, as it is sometimes referred to) is that between the core and conduit when the core is moving inside the conduit. In known control cables, static and dynamic coefficients of friction on the order of 0.22 and 0.29, respectively, are exemplary.
Still another disadvantage of known control cables involves what are known in the industry as "backlash" and "lost motion." Backlash is measured at low cable load and is the motion required (in linear measurement) at the cable input end, i.e., at the control handle end, before motion occurs at the output end. Lost motion involves the same measurement but at high cable load.
Heretofore, designers of control cables have resorted to increasing the radial dimension of the annular space or "gap" between the core and the conduit in an effort to reduce friction and make the core easier to move. But increasing the dimension of such space has the undesirable result of increasing backlash and lost motion. On the other hand, decreases in such radial dimension often resulted in cables which exhibited high friction and were hard to operate.
A new dynamic sealing device and related control cable which addresses the above disadvantages and which makes possible a remote control installation exhibiting improved frictional, column strength and sealing capabilities would be an important advance in the art.